move the headers definition strategy to transport

dart/lib/src/browser_client.dart

@@ -52,7 +52,6 @@ class SentryBrowserClient extends SentryClient {
             clock: options.clock,
             compressPayload: false,
             sdk: Sdk(name: browserSdkName, version: sdkVersion),
-            headersBuilder: SentryClient.buildHeaders,
             platform: platform,
             origin: origin,
           ),

dart/lib/src/client.dart

@@ -163,17 +163,4 @@ abstract class SentryClient {
 
   @override
   String toString() => '$SentryClient("${options.dsn}")';
-
-  @protected
-  static Map<String, String> buildHeaders(String authHeader) {
-    final headers = {
-      'Content-Type': 'application/json',
-    };
-
-    if (authHeader != null) {
-      headers['X-Sentry-Auth'] = authHeader;
-    }
-
-    return headers;
-  }
 }

dart/lib/src/io_client.dart

@@ -31,19 +31,7 @@ class SentryIOClient extends SentryClient {
             clock: options.clock,
             sdk: sdk,
             dsn: options.dsn,
-            headersBuilder: buildHeaders,
             platform: platform,
           ),
         );
-
-  @protected
-  static Map<String, String> buildHeaders(String authHeader) {
-    final headers = SentryClient.buildHeaders(authHeader);
-
-    // NOTE(lejard_h) overriding user agent on VM and Flutter not sure why
-    // for web it use browser user agent
-    headers['User-Agent'] = sdk.identifier;
-
-    return headers;
-  }
 }

dart/lib/src/transport/header_builder.dart

@@ -0,0 +1,17 @@
+import '../protocol.dart';
+
+Map<String, String> buildHeaders(String authHeader, {Sdk sdk}) {
+  final headers = {
+    'Content-Type': 'application/json',
+  };
+
+  if (authHeader != null) {
+    headers['X-Sentry-Auth'] = authHeader;
+  }
+
+  // NOTE(lejard_h) overriding user agent on VM and Flutter not sure why
+  // for web it use browser user agent
+  headers['User-Agent'] = sdk.identifier;
+
+  return headers;
+}

dart/lib/src/transport/header_builder_browser.dart

@@ -0,0 +1,13 @@
+import '../protocol.dart';
+
+Map<String, String> buildHeaders(String authHeader, {Sdk sdk}) {
+  final headers = {
+    'Content-Type': 'application/json',
+  };
+
+  if (authHeader != null) {
+    headers['X-Sentry-Auth'] = authHeader;
+  }
+
+  return headers;
+}

dart/lib/src/transport/transport.dart

@@ -8,15 +8,14 @@ import 'package:sentry/src/utils.dart';
 import '../protocol.dart';
 import '../sentry_options.dart';
 import 'body_encoder_browser.dart' if (dart.library.io) 'body_encoder.dart';
+import 'header_builder_browser.dart' if (dart.library.io) 'header_builder.dart';
 
 typedef BodyEncoder = List<int> Function(
   Map<String, dynamic> data,
   Map<String, String> headers, {
   bool compressPayload,
 });
 
-typedef HeadersBuilder = Map<String, String> Function(String authHeader);
-
 /// A transport is in charge of sending the event to the Sentry server.
 class Transport {
   final Client httpClient;
@@ -25,8 +24,6 @@ class Transport {
 
   final Sdk sdk;
 
-  final HeadersBuilder headersBuilder;
-
   final bool compressPayload;
 
   /// Used by sentry to differentiate browser from io environment
@@ -43,7 +40,6 @@ class Transport {
     @required this.httpClient,
     @required this.sdk,
     @required ClockProvider clock,
-    @required this.headersBuilder,
     @required this.platform,
     this.origin,
   })  : _dsn = Dsn.parse(dsn),
@@ -77,7 +73,9 @@ class Transport {
                 (dsnUri.scheme == 'https' && dsnUri.port != 443))
         ? ':${dsnUri.port}'
         : '';
+
     final pathLength = dsnUri.pathSegments.length;
+
     String apiPath;
     if (pathLength > 1) {
       // some paths would present before the projectID in the dsnUri
@@ -91,6 +89,7 @@ class Transport {
 
   Future<SentryId> send(Map<String, dynamic> data) async {
     final now = _clock();
+
     var authHeader = 'Sentry sentry_version=6, sentry_client=$clientId, '
         'sentry_timestamp=${now.millisecondsSinceEpoch}, sentry_key=$publicKey';
     if (secretKey != null) {
@@ -99,7 +98,7 @@ class Transport {
 
     mergeAttributes(_getContext(now), into: data);
 
-    final headers = headersBuilder(authHeader);
+    final headers = buildHeaders(authHeader, sdk: sdk);
 
     final body = bodyEncoder(data, headers, compressPayload: compressPayload);